The present invention relates in general to semiconductors and, more particularly, to protection circuits for semiconductor devices.
Semiconductor manufacturers are fabricating integrated circuits whose small surface features allow several million transistors to be integrated on a semiconductor die less than one centimeter on a side. These small transistors are highly susceptible to damage from environmental factors such as electrostatic charges. For example, a human body can accumulate enough charge to develop several thousand volts of potential which can permanently damage an integrated circuit. When otherwise functional devices are rendered inoperable due to damage, the effective manufacturing cost increases. The cost is particularly high when the damage occurs late in the fabrication cycle.
To avoid device damage from an electrostatic charge, integrated circuits often include protection circuits to remove the charge before it reaches a damaging voltage level. Prior art protection circuits use large resistors and capacitors to establish a long time constant that maintains the protection circuit in an active state until all of the charge has been removed. However, these large resistors and capacitors occupy a substantial die area, which increases the die size and manufacturing cost of the integrated circuit.
Hence, there is a need for a more economical circuit and method for protecting a semiconductor device from damage due to high voltage developed by an electrostatic charge applied to the device.